Pitx1 determines the morphology of muscle, tendon, and bones of the hindlimb

Abstract

The shapes of homologous skeletal elements in the vertebrate forelimb and hindlimb are distinct, with each element exquisitely adapted to their divergent functions. Many of the signals and signalling pathways responsible for patterning the developing limb bud are common to both forelimb and hindlimb. How disparate morphologies are generated from common signalling inputs during limb development remains poorly understood. We show that, similar to what has been shown in the chick, characteristic differences in mouse forelimb and hindlimb cartilage morphology are maintained when chondrogenesis proceeds in vitro away from the endogenous limb bud environment. Chondrogenic nod-ules that form in high-density micromass cultures derived from forelimb and hindlimb buds are consistently different in size and shape. We described analytical tools we have developed to quantify these differences in nodule morphology and demonstrate that characteristic hindlimb nodule morphology is lost in the absence of the hindlimb-restricted limb modifier gene Pitx1. Furthermore, we show that ectopic expression of Pitx1 in the forelimb is sufficient to generate nodule patterns characteristic of the hindlimb. We also demonstrate that hindlimb cells are less adhesive to the tissue culture substrate and, within the limb environment, to the extracellular matrix and to each other. These results reveal autonomously programmed differences in forelimb and hindlimb cartilage precursors of the limb skeleton are controlled, at least in part, by Pitx1 and suggest this has an important role in generating distinct limb-type morphologies. Our results demonstrate that the micromass culture system is ideally suited to study cues governing morphogenesis of limb skeletal elements in a simple and experimentally tractable in vitro system that reflects in vivo potential.

Deletions in PITX1 cause a spectrum of lower-limb malformations including mirror-image polydactyly

“…This and the finding that Pitx1 is expressed only in the hindlimb suggested a role in the determination of hindlimb morphology and identity. [11][12][13][14] The hypothesis was supported by studies performed in chick and mouse showing that misexpression of Pitx1 in forelimbs results in the adoption of hindlimb characteristics. 14,15 In fish, pelvic loss in different natural populations of stickleback fish has occurred through regulatory mutations deleting a tissue-specific enhancer of Pitx1 and demonstrates an evolutionary change in vertebrates via this genomic region.…”

“…[11][12][13][14] The hypothesis was supported by studies performed in chick and mouse showing that misexpression of Pitx1 in forelimbs results in the adoption of hindlimb characteristics. 14,15 In fish, pelvic loss in different natural populations of stickleback fish has occurred through regulatory mutations deleting a tissue-specific enhancer of Pitx1 and demonstrates an evolutionary change in vertebrates via this genomic region. 16 In humans, a missense mutation (p.E130K) in PITX1 has been shown to segregate with dominantly inherited clubfoot with reduced penetrance in a large kindred, together with unilateral tibial hemimelia and preaxial polydactyly in one individual in this family.…”

“…This hypothesis is corroborated by Shh expression analysis showing normal patterns of Shh expression in the ZPA of Pitx1 À/À mice. 12 Only a combined inactivation of Pitx1 and Pitx2 resulted in abnormal Shh expression and Pitx1 overexpression in the forelimb caused downregulation of Shh, 14 indicating some degree of interaction between the pathways. A similar discrepancy between mouse and human phenotypes has been observed for WNT7A.…”

Expression of pituitary homeobox 1 gene in human gastric carcinogenesis and its clinicopathological significance

“…Besides sharing similar DNA binding specificities, PITX1 and PITX2 are co-expressed in the stomodeum and have overlapping expression patterns in stomodeal derivatives [11][12][13] . Specifically, PITX1 is responsible for the morphology of muscles, tendons and the bones of hind limbs, and is involved in the development of anterior structures as well as pituitary and craniofacial morphogenesis [14,15] .…”

Three-Dimensional (3D) Visualisation of the Cardiovascular System of Mouse Embryos and Fetus

“…This sets an upper specimen size limit. Mouse embryos, especially early embryos are small enough to become 3D visualised with OPT [73,[78][79][80]. Late mouse embryos and mouse fetus must be parted or dissected prior to staining and scanning (e.g.…”